1. Field of the Invention
The present invention relates to a semiconductor memory device, and more particularly to, e.g., a semiconductor memory device including a variable-resistance element whose resistance varies based on stored data.
2. Description of the Related Art
As a memory using a variable-resistance element, for example, a magnetic random access memory (MRAM), phase-change random access memory (PCRAM), or resistive random access memory (ReRAM) is known. A memory cell used in each of these memories has a configuration where one variable-resistance element and one select transistor are connected in series, for example. Further, a bit line is connected to the other end of the variable-resistance element, a word line is connected to a gate of the select transistor, and a ground terminal is connected to the other end of the select transistor.
When reading data stored in this memory cell, a read voltage is applied to the memory cell, for example. Furthermore, the resistance state of the memory cell is determined to read the data by using a sense amplifier to compare a read current flowing through the memory cell with a reference current. Here, in order to perform accurate reading, the read voltage must be kept constant even when there is power supply noise.
Moreover, as this type of relevant technology, a technology that uses a dummy cell to generate a reference current which is utilized when reading data is suggested (JP-A 2003-297072 [KOKAI]).